package middle;

/**
 * JD4 上台阶
 * @author d3y1
 */
public class JD4{
    private static final int MOD = 1000000007;

    /**
     * 动态规划
     *
     * dp[i]表示到达第i级的走法数
     *
     * 举例子找规律
     * dp[i] = dp[i-1] + dp[i-2]
     *
     * @param n
     * @return
     */
    public int countWays(int n) {
        if(n == 1){
            return 0;
        }

        int[] dp = new int[n+1];
        dp[1] = 1;
        dp[2] = 1;
        for(int i=3; i<=n; i++){
            dp[i] = (dp[i-1] + dp[i-2])%MOD;
        }

        return dp[n];
    }
}